1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine.
2. Related Background Art
Since various kinds of originals or manuscripts need to be copied and various kinds of images are requested by operators, not only a popular monochromatic copy which is normally and widely used, but also colored copies (that is, an image is formed with colors such as red, blue and the like by means of an image forming apparatus) have recently been requested.
In order to meet such requests, as shown in FIG. 2, an image forming apparatus wherein a plurality of developer containers each including developer of a different color such as red, blue, green and the like are used and these developer containers can be automatically changed as needed by an operator, thus permitting the formation of multi-colored images.
In FIG. 2, an original 2 positioned on an original support glass 1 is illuminated by a lamp 3 to create a light image. The light image is directed to a photosensitive drum 11 through an optical system comprising reflection mirrors 4, 5, 6, 7, 8, and 9, and a zoom lens 10. The lamp 3, mirror 4 and mirrors 5, 6 are shifted at a predetermined speed in a direction shown by an arrow, to scan the original 2. Since the photosensitive drum 11 is rotated in a direction shown by an arrow, after charges are uniformly applied to an outer surface of the drum by a primary charger 12, electrostatic latent images corresponding to the original images are sequentially formed on the surface of the drum 11.
In association with the photosensitive drum 11, color developer containers 13B, 13C, 13D each containing colored toner (such as red toner, blue toner, green toner) and a black developer container 13A containing black toner are arranged. These developer containers 13A, 13B, 13C and 13D can be shifted in an up-and-down direction and in a direction shown by an arrow. The developer container corresponding to a desired color image is shifted to a desired level and then is shifted toward the photosensitive drum 11 to a developing station, where the electrostatic latent image is visualized by the colored toner contained in such developer container. The visualized or developed image is transferred onto a sheet, i.e., transfer paper 17 by a transfer charger 15. Thereafter, the photosensitive drum 11 is rotated to a cleaning station, where the residual toner remaining on the drum surface is removed by a cleaner 16 to prepare for the next copying cycle.
The transfer paper or sheet 17 can be fed into the copying machine by any one of the following methods.
In a first method, the transfer papers 17 stacked in a sheet cassette 18 are fed one by one toward a pair of rollers 20 by means of a pick-up roller 19. If a plurality of transfer papers 17 are fed in an overlapped condition to the paired rollers 20, these rollers can separate, an uppermost transfer paper from the others to feed only one transfer paper into the machine. After passing through the paired rollers 20, the transfer paper 17 is fed to resist rollers 23 through guide plates 21, 22, a pair of feed rollers 50 and guide plates 52, 53, 51.
In a second method, the transfer papers 17 stacked in a sheet cassette 24 are fed one by one toward a pair of rollers 26 by means of a pick-up roller 25. The paired rollers 26 have the same function as that of the aforementioned paired rollers 20. After passing through the paired rollers 26, the transfer paper 17 is fed to the resist rollers 23 through guide plates 27, 28, paired feed rollers 50 and guide plates 52, 53, 51. The resist rollers 23 are rotated synchronously with the rotation of the photosensitive drum 11 so that the transfer paper 17 fed to the, photosensitive drum 11 from the resist roller 23 through an upper guide 31 and a lower guide 32 mates with the visualized image on the drum.
As mentioned above, the image on the photosensitive drum 11 is transferred onto the transfer paper 17 by the transfer charger 15. Thereafter, the transfer paper 17 is separated from the drum surface by means of separating charger 33. Then, the transfer paper is fed, through a feeding means 34, to a fixing device 35 including a heating roller 35a and a pressure roller 35b. The image transferred on the transfer paper 17 is heated and pressurized in the fixing device 35 to be fixed on the transfer paper 17 as a permanent image. Then, the transfer paper 17 is fed to a first ejector or discharge roller 36, from which location the transfer sheet is fed to a second ejector roller 39 through flappers 37 and 38. The transfer paper is ejected from the copying machine by this second ejector roller. Incidentally, in FIG. 2, although the flapper 38 is shown to block a transfer paper feeding path, the flapper 38 is made of light-weighted material and is freely rotatable in a direction shown by an arrow (i.e., in a clockwise direction). Accordingly, when the transfer paper 17 encounters the flapper 38, the latter is pushed up by a leading edge of the transfer paper 17, and thus is rotated in a clockwise direction to a retracted position to permit the passing of the transfer paper.
Further, the above-mentioned copying machine has a both-side copying function and a multiple copying function. Next, fundamental feeding operations regarding the transfer paper in these functions will be explained.
When the both-side (both-surface) copying function is selected in the copying machine, the transfer paper 17 is moved up to the second ejector roller 39 in the same fundamental manner as that mentioned above, meanwhile the image is, transferred onto one surface of the transfer paper 17 and is fixed thereto as mentioned above. While the transfer paper 17 is being ejected from the copying machine, if a predetermined time interval elapses after a trailing edge of the transfer paper 17 is detected by a sheet detecting mechanism comprising a detection lever 40 and a photosensor 41 (i.e., when the trailing edge of the transfer paper 17 has passed the flapper 38), the second ejector roller 39 is rotated in a reverse direction, thus introducing the transfer paper 17 into the copying machine again.
The transfer paper 17 then advances toward the inside of the copying machine with directing the trailing edge thereof in a forward direction, and is guided by the left inclined surfaces of the flappers 38, 37, guide plates 42, 43, 44, 44' and rollers 100 to reach rollers 45. Thereafter, the transfer paper 17 reaches re-feed rollers 47 through rollers 46. At this point, the re-feed rollers 47 are stopped. After the transfer paper completely abuts against the rollers 47, the paired rollers 45, 46 are also stopped, thus waiting for a new copying operation regarding the other surface of the transfer paper 17. When a copy start signal regarding the other surface of the transfer paper 17 is emitted or discharged, the re-feed rollers 47 start to rotate, whereby the transfer paper 17 is fed to the resist rollers 23 through guide plates 48 and 49. Then, a new image is transferred onto the other surface of the transfer paper 17 and is fixed thereto in the same fundamental manner as mentioned above. The transfer paper 17 on both surfaces of which the images are copied is finally ejected from the copying machine by means of the second ejector roller 39.
On the other hand, when the multiple copying function is selected in the copying machine, in a first copying cycle, an image is transferred onto the transfer paper 17 and is fixed thereto in the same fundamental manner as mentioned above. In the multiple copying function, the flapper 37 is positioned in a position shown by a broken line in FIG. 2. Accordingly, the transfer paper 17 fed by the first ejector roller 36 directing the leading edge thereof in a forward direction, is fed to the guide plates 42, 43 along a right inclined surface of the flapper 37, and then is fed to the paired rollers 45 through the guide plates 44, 44' and the paired rollers 100. Thereafter, the transfer paper 17 reaches the pair of re-feed rollers 47 through the paired rollers 46. When a predetermined time period has elapsed after the trailing edge of the transfer paper 17 is detected by the detection lever 40 and the photosensor sensor 41, the flapper 37 is returned, to a position shown by a solid line in FIG. 2. When a second copying signal is emitted, the re-feed rollers 47 start to rotate, whereby the transfer paper 17 is fed to the photosensitive drum 11 in the same manner as in the case of the both-side copying function, wherein a new image is transferred onto the same surface of the transfer paper 17 as the surface on which the image is transferred in the first copying cycle. Thereafter, the transfer paper on the surface of which multiple images are copied is finally ejected from the copying machine by means of the second ejector roller 39.
When the multi-colored image is formed on the transfer paper by using such copying machine, fundamentally, the copying cycles are repeated per the used color toners (developer containers including such color toners). For example, in order to obtain a copied image including three colors of green, red and blue, firstly, an image is formed on the transfer paper 17 with green color toner by using the developer container 13C, then the same transfer paper 17 is fed to the image forming portion (photosensitive drum) again through a transfer paper feeding path shown by a letter A (FIG. 2). Then, the developer container 13C is changed to the developer container 13B, and a new image is formed on the same transfer paper with red color toner. And, similarly, a new image is formed on the same transfer paper with blue color toner (included in the developer container 13D) to complete the three colored image.
While an example of the three colored image being formed on a single transfer paper was explained above, when the same three colored images are to be formed on n (in number) transfer papers, it is necessary to repeat the above-mentioned copying cycles n times in the aforementioned conventional copying machine. Consequently, in the conventional copying machine, the developer containers must be changed three times each time the colored image is formed on the single transfer paper, thus increasing the total copying time.
Conventional copying machines which can obtain a plurality of both side and/or multiple copies by providing an intermediate tray for both-side copying and multiple copying functions have been proposed. However, each of these conventional copying machines is only effective to form two images. Both-side copying function and multiple (only two) copying function, i.e., to form only two images in total, cannot obtain a plurality of copies using the single intermediate tray, where an image is formed in three or more copying cycles, since both a transfer paper used for the next image forming operation and a transfer paper on which the image is already formed used for the next copying cycle, cannot be contained in the same intermediate tray.
In order to solve this problem, a copying machine having a plurality of intermediate trays has been proposed (for example, as disclosed in the Japanese patent Application Laid-Open No. 62-293258). In this conventional copying machine, two (first and second) intermediate trays are provided, and the above-mentioned transfer paper on which, the image is already formed and which is used for the next copying cycle is received in the second intermediate tray, thus preventing the mixing of two kinds of transfer papers, whereby n (in number) colored image can be formed on a single transfer paper or an image can be formed on a single transfer paper in n (in number) copying cycles, for a plurality of transfer papers, thereby reducing the total copying time.
However, in this conventional copying machine, since two intermediate trays are used, the whole copying machine will be large in size and expensive, thus limiting the usage thereof and making wide use thereof difficult.
In such a conventional copying machine, when a plurality of copies are obtained by performing three or more copying cycles for each transfer sheet, the intermediate trays cannot be used and the copying cycles must be repeated for each copy or transfer paper, thus increasing the total copying time. In addition, in the case where different originals are to be used, the originals must be changed per each image forming operation, resulting in making troublesome and increasing the copying time. Further, since the original is repeatedly used, the damage of the originals is not negligible.
In order to eliminate the above-mentioned drawbacks, a copying machine having three or more intermediate trays has been proposed. However, in this case, of course, the whole machine would be large and expensive, thus preventing the wide use thereof.